Recessed thin-channel thin-film transistor

ABSTRACT

A thin-film transistor includes a gate electrode, a gate dielectric on the gate electrode, a first layer including a source region, a drain region, and a semiconductor region above and in direct contact with the gate dielectric and physically connecting the source and drain regions, and a second layer including an insulator material on the semiconductor region. The semiconductor region has less vertical thickness than the source and drain regions. In an embodiment, the thickness of the semiconductor region is no more than half that of the source and drain regions. In another embodiment, the second layer physically connects and electrically separates the source and drain regions. In yet another embodiment, a memory cell includes this transistor and a capacitor electrically connected to the drain region, the gate electrode being electrically connected to a wordline and the source region being electrically connected to a bitline.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a U.S. National Phase Application under 35U.S.C. § 371 of International Application No. PCT/US2017/056296, filedon Oct. 12, 2017, the entire contents of which is hereby incorporated byreference herein.

BACKGROUND

A thin-film transistor (TFT) is generally fabricated by depositing thinfilms of an active semiconductor layer as well as a dielectric layer andmetallic contacts over a substrate. There are a number of non-trivialperformance issues associated with TFTs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an example recessed thin-channelthin-film transistor (TFT), according to an embodiment of the presentdisclosure.

FIG. 2 is a cross-sectional view of an example embedded memory cellhaving a stacked capacitor with a recessed thin-channel TFT, accordingto an embodiment of the present disclosure.

FIG. 3 is a cross-sectional view of an example embedded memory cellhaving a U-shaped capacitor with a recessed thin-channel TFT, accordingto an embodiment of the present disclosure.

FIG. 4 is a cross-sectional view of an example recessed thin-channelTFT-based embedded memory, according to an embodiment of the presentdisclosure.

FIG. 5 is an example gate length-subthreshold swing (SS) curve andcomparison curve for driving a recessed thin-channel TFT, according toan embodiment of the present disclosure.

FIGS. 6A-6G are cross-sectional views illustrating an example method offabricating a recessed thin-channel TFT, according to an embodiment ofthe present disclosure.

FIG. 7 is a schematic plan view of an example recessed thin-channelTFT-based embedded memory configuration, according to an embodiment ofthe present disclosure.

FIG. 8A is a plan view of an example layout of an embedded memorywithout overlap of the memory array and memory peripheral circuit.

FIGS. 8B-8C are plan views of an example layout of a recessedthin-channel TFT-based embedded memory with overlap of the memory arrayand memory peripheral circuit, according to an embodiment of the presentdisclosure.

FIG. 9 illustrates an example method of fabricating a recessedthin-channel TFT-based memory array, according to an embodiment of thepresent disclosure.

FIG. 10 illustrates an example computing system implemented with theintegrated circuit structures or techniques disclosed herein, accordingto an embodiment of the present disclosure

These and other features of the present embodiments will be understoodbetter by reading the following detailed description, taken togetherwith the figures herein described. In the drawings, each identical ornearly identical component that is illustrated in various figures may berepresented by a like numeral. For purposes of clarity, not everycomponent may be labeled in every drawing. Furthermore, as will beappreciated, the figures are not necessarily drawn to scale or intendedto limit the described embodiments to the specific configurations shown.For instance, while some figures generally indicate straight lines,right angles, and smooth surfaces, an actual implementation of thedisclosed techniques may have less than perfect straight lines and rightangles, and some features may have surface topography or otherwise benon-smooth, given real-world limitations of fabrication processes. Inshort, the figures are provided merely to show example structures.

DETAILED DESCRIPTION

According to various embodiments of the present disclosure, a recessedthin-channel thin-film transistor (TFT) is provided. The recessedthin-channel TFT may be formed by recessing the back-channel of the TFT.This can improve electrostatics and short-channel control while reducingor eliminating the need for targeting of contact etches, such as sourceand drain contact etches. In addition, the recession can be performedafter source and drain electrode formation, which can allow for aself-aligned process. In some embodiments, the channel region is thinner(e.g., has less vertical thickness) than the source and drain regions.For example, in some embodiments, the channel region is recessed morethan the source or drain regions (for example, to provide better gatecontrol and improve any short-channel effects). In some embodiments, therecessed thin-channel region in the TFT provides for longer effectivechannel length L_(eff) as well as better threshold voltage V_(t)roll-off and subthreshold swing (SS) roll-off. Such recessedthin-channel TFTs can be useful in memory applications, such as dynamicrandom-access memory (DRAM), and as backend TFTs in back end of line(BEOL) devices such as embedded DRAM (eDRAM).

General Overview

As noted above, there are a number of non-trivial performance issuesassociated with thin-film transistors (TFTs). For instance, TFTs withthick bodies do not have good electrostatic gate control. Such devicescan suffer from subthreshold swing (SS) degradation and lead tohigh-voltage devices. Moreover, depositing thin TFT channel materialscan make damascene contact etch very challenging due to the aggressiveetch chemistry involved. For example, if the layers (e.g., semiconductoror active layers) are too thin, they can be blown through duringsubsequent processing such as chemical mechanical planarization (CMP),which can have little to no selectivity and can inadvertently removeextra channel material, compromising the TFTs. In general, thickersemiconductor (active) layers (bodies) in TFTs lead to poorer gatecontrol, performance, and voltage levels. While thick bodies may beneeded in TFTs (e.g., for copper interconnect processes such asdamascene and chemical mechanical planarization), thinning the channelregion (such as the back-channel) with respect to the source and drainregions can reduce or eliminate some or all of the degrading thick-bodyeffects. In addition, often, the back-channel interface in such devicesis degraded due to passivation and may benefit from cleaning throughthinning.

Accordingly, in various embodiments of the present disclosure, theback-channel of a TFT (such as a bottom gate TFT) is recessed withrespect to the neighboring source and drain regions of the semiconductor(active) layer. The recession, for example, can be performed in aself-aligned process after source and drain electrode formation byetching the exposed channel region (e.g., an exposed portion of thechannel region) between the source and drain electrodes. Afterwards, apassivation or capping layer including an electrical insulator materialcan be formed on the recessed channel region to physically connect andelectrically separate the exposed sides of the source and drain regions.

According to various embodiments, the channel thickness after therecession can be, for example, a particular fraction of the source anddrain thickness (such as half or less of the source and drain thickness,e.g., one third, one quarter). Here, channel thickness is in thevertical direction (e.g., perpendicular to the substrate of anintegrated circuit incorporating the TFT). In some embodiments, thechannel thickness after the recession can be an absolute thickness, suchas between 5 and 20 nanometers (nm), or between 7 and 15 nm, or someparticular thickness such as 10 nm. For example, a 40 nm semiconductorlayer can be recessed to 20 nm (e.g., about half the height or thicknessof the source and drain regions) in some embodiments, to 14 nm (e.g.,about a third of the source and drain thickness) in some otherembodiments, and to 10 nm (e.g., about a quarter of the source and drainheight) in still some other embodiments. However, since benefits accruefor even small amounts of recession (e.g., less removal of channelregion material), in some embodiments, the channel is only thinned to 30nm (e.g., about three quarters of the source and drain thickness).

In an example embodiment of the present disclosure, a recessedthin-channel thin-film transistor (TFT) includes a gate electrode, agate dielectric on the gate electrode, an active layer including asemiconductor material on the gate electrode, and a capping layerincluding an insulator material on the active layer. The active layerincludes a source region, a drain region, and a semiconductor regionabove and in direct contact with the gate dielectric and physicallyconnecting the source and drain regions (e.g., as separate structures,as separate regions of the same structure, as separate regions of thesame layer, or the like). For instance, each of the source and drainregions can be adjacent to (e.g., physically part of or connecting) adifferent portion (e.g., a different end or side) of the semiconductorregion. The semiconductor region is thinner than the source and drainregions. The capping layer is on the semiconductor region, andphysically connects as well as electrically separates the source anddrain regions. In an embodiment, the TFT further includes source anddrain electrodes electrically connected to the source and drain regions,respectively, with the capping layer physically connecting andelectrically separating the source and drain electrodes.

In one or more embodiments, a memory cell includes this TFT, with thegate electrode being electrically connected to a wordline and the sourceregion being electrically connected to a bitline. The memory cellfurther includes a capacitor including a first terminal electricallyconnected to the drain region, a second terminal, and a dielectricmedium electrically separating the first and second terminals. In someembodiments, a memory array includes a plurality of wordlines extendingin a first direction, a plurality of bitlines extending in a seconddirection crossing the first direction, and a plurality of such memorycells at crossing regions of the wordlines and the bitlines. In someembodiments, the memory array is an embedded memory, e.g., formed in theBEOL process above and electrically connected to frontend orfront-end-of-line (FEOL) circuits including memory control circuits suchas wordline drivers (electrically connected to the wordlines) and senseamplifiers (electrically connected to the bitlines). In this fashion,the BEOL circuits (memory array) can overlay the FEOL circuits (memorycontrol) and save integrated circuit planar area. As such, embodimentsof the present disclosure can be applied to smaller processtechnologies, such as 14 nanometer (nm), 10 nm, 7 nm, 5 nm, and beyond.

Architecture and Methodology

FIG. 1 is a cross-sectional (X-Z) view of an example recessedthin-channel thin-film transistor (TFT) 100, according to an embodimentof the present disclosure. Throughout, the z-axis represents a verticaldimension (e.g., perpendicular to an integrated circuit substrate),while the x- and y-axes represent horizontal dimensions (e.g., parallelto the wordline and bitline directions, respectively). The components ofTFT 100 can be fabricated using semiconductor fabrication techniques,such as deposition and photolithography. The components of TFT 100 canbe part of a backend process, such as the back end of line (BEOL)process of a semiconductor integrated circuit. As such, the componentsof TFT 100 can be fabricated as part of, or concurrently with, the metalinterconnection layers (such as the upper or middle metalinterconnection layers) of a semiconductor fabrication process. In someother embodiment, the components of TFT 100 are fabricated as part of afront end of line (FEOL) process (e.g., on a substrate instead of theILD 110).

In example embodiments, fabrication of the components of TFT 100 can bepart of the metal 4 (interconnect) layer of a BEOL process, using mostlya custom process (e.g., separate from the other metal 4 features) toform the components. Referring to FIG. 1, a gate (or gate electrode) 120is formed, such as on an interlayer dielectric (ILD, such as an etchstop material) 110. The gate 120 is conductive, and can represent one ormore layers or features for supplying a gate signal to the TFT 100. Forinstance, the gate 120 can include a wordline (such as a wordline madeof copper (Cu) or aluminum (Al)) to supply a gate signal from a wordlinedriver, along with diffusion barriers and a metal gate electrode forsupplying the gate signal to the proximity of the channel region 146 ofthe TFT 100.

For example, the gate 120 can include thin-film layers such as one ormore gate electrode layers (e.g., diffusion barrier and metal gatelayers). The diffusion barrier can be a metal- or copper-diffusionbarrier (e.g., a conductive material to reduce or prevent the diffusionof metal or copper from a wordline into the metal gate 120 while stillmaintaining an electrical connection between the wordline and the metalgate 120) on the wordline such as tantalum nitride (TaN), tantalum (Ta),titanium zirconium nitride (e.g., Ti_(X)Zr_(1-X)N, such as X=0.53),titanium nitride (e.g., TiN), titanium tungsten (TiW), combination (suchas a stack structure of TaN on Ta), or the like.

For instance, the diffusion barrier can include a single- or multi-layerstructure including a compound of tantalum (Ta) and nitrogen (N), suchas TaN or a layer of TaN on a layer of Ta. In some embodiments, a layerof etch-resistant material (e.g., etch stop) such as silicon nitride(e.g., Si₃N₄) or silicon carbide (e.g., SiC) is formed over the wordlinewith vias for a metal (or copper) diffusion barrier film such as TaN ora TaN/Ta stack. The metal gate can be a conductive material on thediffusion barrier, such as metal, conductive metal oxide or nitride, orthe like. For example, in one embodiment, the metal gate is titaniumnitride (TiN). In another embodiment, the metal gate is tungsten (W).

The gate 120 is covered with a gate dielectric 130 corresponding to anactive (semiconductor) layer 140 (or to a channel area 146 of the activelayer) of the TFT 100. The gate dielectric 130 can be a high-κdielectric material such as hafnium dioxide (HfO₂). The gate dielectric130 can be thin, such as 4 nanometers (nm). In some embodiments, thegate dielectric 130 is in a range of 3 nm to 7 nm. In some embodiments,the gate dielectric 130 is in a range of 2 nm to 10 nm. In someembodiments, the gate dielectric 130 can be silicon dioxide (SiO₂),silicon nitride (e.g., Si₃N₄), hafnium dioxide (HfO₂) or other high-κmaterial, or a multi-layer stack including a first layer of SiO₂ and asecond layer of a high-κ dielectric such as HfO₂ on the SiO₂. Any numberof gate dielectrics can be used, as will be appreciated in light of thepresent disclosure. For example, in one embodiment, the gate dielectric130 is a layer of SiO₂. In another embodiment, the gate dielectric 130is a stack (e.g., two or more layers) of HfO₂ on SiO₂.

The semiconductive active layer 140 is formed over the gate dielectric130. The active layer 140 can be formed in a backend process, forexample, from one or more of indium gallium zinc oxide (IGZO), indiumzinc oxide (IZO), amorphous silicon (a-Si), low-temperaturepolycrystalline silicon (LTPS), and amorphous germanium (a-Ge). Forexample, the active layer 140 can be IGZO or the like in contact with abitline (such as at a source region 142 of the active layer 140) and astorage node (e.g., at a drain region 144 of the active layer 140), witha semi-conductive channel region 146 between and physically connectingthe drain region 144 and the source region 142. Such an active layerchannel 146 may include only majority carriers in the thin film.Accordingly, the active layer channel 146 may require high bias (assupplied by the wordline, diffusion barrier film, and metal gate) toactivate.

In various embodiments of the present disclosure, the channel region 146in the recessed thin-channel TFT 100 is recessed (e.g., etched) withrespect to the source and drain regions 142 and 144. For example, anactive layer 140 can be formed as a semiconductor layer, the source anddrain regions 142 and 144 of the semiconductor layer appropriatelydoped, and the channel region 146 thinned (e.g., to half or less of thethickness of the source and drain regions 142 and 144). In someembodiments, source and drain electrodes 150 and 160 are formed aboveand electrically connected to the source and drain regions 142 and 144,respectively (e.g., through contact etching), and then the channelregion 146 is thinned through etching using the source and drainelectrodes 150 and 160 to self-align the process.

The source and drain electrodes 150 and 160 can be formed by, forexample, contact etching the source and drain regions 142 and 144,respectively. In some embodiments, a contact metal is annealed, etched,or otherwise formed on or combined with the tops of the source and drainregions 142 and 144 to make contacts, such as silicide (or otherappropriate compound, depending on the contact metal) contacts with theactive layer 140 material. Example contact metals include titaniumnitride (e.g., TiN, TiN_(x) with 0.6≤x≤1.2), copper (Cu), tungsten (W),titanium oxynitride (e.g., TiO_(x)N_(y) with x>0 and y>0), titanium(Ti), tantalum (Ta), tantalum nitride (e.g., TaN), aluminum titaniumnitride (e.g., AlTi_(x)N_(y) with 0<x<1 and y>0), tantalum titaniumnitride (e.g., TaTi_(x)N_(y) with x>0 and y>0), aluminum tantalumnitride (e.g., AlTa_(x)N_(y) with x>0 and y>0), tungsten nitride (e.g.,W₂N, WN, WN₂), indium arsenide (e.g., InAs), and indium oxide (e.g.,In₂O₃, InO_(x) with x>0), to name a few. The source and drain electrodes150 and 160 can then be formed on the contacts.

In addition to IGZO, in some embodiments, the active layer 140 is one ofa variety of polycrystalline semiconductors, including, for example,zinc oxynitride (ZnON, such as a composite of zinc oxide (ZnO) and zincnitride (Zn₃N₂), or of ZnO, ZnO_(x)N_(y), and Zn₃N₂), indium tin oxide(ITO), tin oxide (e.g., SnO), copper oxide (e.g., Cu₂O), polycrystallinegermanium (poly-Ge) silicon-germanium (e.g., SiGe, such asSi_(1-x)Ge_(x)) structures (such as a stack of poly-Ge over SiGe), andthe like. In some embodiments, the active layer 140 is formed from firsttype channel material, which may be an n-type channel material or ap-type channel material. An n-type channel material may include one ormore of indium tin oxide (ITO), indium gallium zinc oxide (IGZO), indiumzinc oxide (IZO), aluminum-doped zinc oxide (AZO), amorphous silicon,zinc oxide, amorphous germanium, polysilicon, poly germanium, andpoly-III-V like indium arsenide (e.g., InAs). On the other hand, ap-type channel material may include one or more of amorphous silicon(a-Si), zinc oxide (e.g., ZnO), amorphous germanium (a-Ge), polysilicon(polycrystalline silicon or poly-Si), poly germanium (polycrystallinegermanium or poly-Ge), poly-like InAs, copper oxide (CuO), and tin oxide(SnO). In some embodiments, the channel region 146 can have a thicknessin a range of about 5 nm to about 50 nm.

As mentioned, the active layer 140 can be divided into three differentregions, namely the source and drain regions 142 and 144 with thechannel region 146 between and physically connecting the source anddrain regions 142 and 144. The active layer 140 forms a transistordevice with the gate 120 and gate dielectric 130. When a gate signal issupplied to the gate 120, the active layer 140 becomes conductive, andcurrent flows between the source and drain regions 142 and 144 via thechannel region 146.

Above the channel region 146, a capping layer (or passivation layer) 170is formed, between the source and drain regions 142 and 144, and betweenthe source and drain electrodes 150 and 160. The capping layer 170includes an insulator material, and forms a good interface with theactive layer 140 materials, preventing leakage and being hermetic toother metal layers or features. In some embodiments, the capping layer170 physically connects and electrically separates the source and drainregions 142 and 144 as well as the source and drain electrodes 150 and160. In some embodiments, the capping layer 170 includes an insulatormaterial, such as aluminum oxide (e.g., Al₂O₃), gallium oxide (e.g.,Ga₂O₃), silicon nitride (e.g., Si₃N₄, SiN), silicon dioxide (SiO₂),titanium dioxide (TiO₂), hafnium dioxide (HfO₂), silicon oxynitride(e.g., Si₂N₂O, SiO_(x)N_(y) with 0≤x≤2 and 0≤y≤4/3), aluminum silicate(e.g., Al₂O₃(SiO₂)_(x) with x>0), tantalum oxide (e.g., Ta₂O₅), hafniumtantalum oxide (e.g., HfTa_(x)O_(y) with x>0 and y>2), aluminum nitride(e.g., AlN), aluminum silicon nitride (e.g., AlSi_(x)N_(y) with x>0 andy>1), sialon (e.g., AlSi_(x)O_(y)N_(z) with x>0, y>0, and z>0),zirconium dioxide (ZrO₂), hafnium zirconium oxide (e.g., HfZr_(x)O_(y)with x>0 and y>2), tantalum silicate (e.g., TaSi_(x)O_(y) with x>0 andy>0), hafnium silicate (e.g., HfSiO₄, HfSi_(x)O_(y) with x>0 and y>2),or the like.

For instance, in some embodiments, the capping layer includes one ormore of aluminum oxide, silicon nitride, titanium dioxide, hafniumdioxide, silicon oxynitride, and aluminum nitride. The source electrode150 is formed and electrically connected to the source region 142 andthe drain electrode 160 is formed and electrically connected to thedrain region 144. The source and drain electrodes 150 and 160 can bemetal, such as metal interconnect layer material (e.g., Cu, Al, ortungsten (W)). The thin-channel TFT 100 acts as a switch, electricallyconnecting the source and drain electrodes 150 and 160 in response to agate signal, such as a gate signal being supplied to the gate 120.

FIG. 2 is a cross-sectional (X-Z) view of an example embedded memorycell 200 having a stacked capacitor 290 with a recessed thin-channel TFT(such as the recessed thin-channel TFT 100 of FIG. 1), according to anembodiment of the present disclosure. In FIG. 2, a metal bitline 270(e.g., metal interconnect material, such as copper, aluminum, ortungsten) is formed on the source electrode 150. The bitline 270 isused, for example, to program or sense the capacitance of the capacitor290 through the source region 142 of the recessed thin-channel TFT 100when the TFT 100 is turned on. In addition, a storage node 280 (e.g.,further metal interconnect material) is formed on the drain electrode160. The storage node 280 electrically connects the drain electrode 160to the capacitor 290 to write (e.g., program) or read (e.g., sense) thecapacitance (e.g., logical 1 or 0) of the capacitor 290 (e.g., throughthe bitline 270 when the thin-channel TFT 100 is turned on).

In some embodiments, the bitline 270 is used in combination with thestorage node 280 to program or sense the state of a capacitor when thethin-channel TFT 100 is used as part of a memory device (such as a DRAMcell). In some other embodiments, the thin-channel TFT 100 acts as aswitch, controlling an electrical current between the storage node 280and bitline 270. In some embodiments, the roles of the source and drainelectrodes 150 and 160 are reversed, the drain electrode 160 beingconnected to the bitline 270 and the source electrode 150 beingconnected to the storage node 280.

The stacked capacitor 290 is formed in layers (e.g., as part of a BEOLprocess, such as part of the metal 6 interconnect layer). The capacitor290 includes a first terminal 292, a dielectric (or dielectric medium)296 on the first terminal 292, and a second terminal 294 on the on thedielectric 296. The first and second terminals 292 and 294 can be metalsor other conductive materials (e.g., metal, conductive metal nitride orcarbide, or the like), while the dielectric 296 can be an insulator toelectrically separate the first and second terminals 292 and 294,allowing a capacitance to be formed between the first and secondterminals 292 and 294. The first terminal 292 is electrically connectedto the drain electrode 160 via the storage node 280. The second terminal294 can be electrically connected, for example, to a common orprogrammable voltage (such as a ground voltage), or to a plate line(e.g., to all the memory cells 200 sharing the same wordline driving thegate 120) for supplying a common or programmable voltage.

In further detail, in one embodiment, the first terminal 292 is tantalum(Ta). In another embodiment, the first terminal 292 is titanium nitride(TiN). In some embodiments, the first terminal 292 is titanium aluminumnitride (e.g., TiAlN, where the molar amount of titanium is at leastthat of aluminum). In another embodiment, the first terminal 292 istantalum aluminum carbide (TaAlC). In another embodiment, the firstterminal 292 is tantalum nitride (TaN). For example, in one embodiment,the second terminal 292 is TiN. For example, in one embodiment, thedielectric 296 is SiO₂. In some embodiments, such as to reduce tunneling(e.g., when the dielectric 296 is very thin), the dielectric 296 is ahigh-κ dielectric material such as zirconium dioxide (ZrO₂) or aluminumoxide (Al₂O₃).

The first terminal 292 of the capacitor 290 connects to a correspondingstorage node 280 through the storage node 280. The first terminals 292of multiple such capacitors 290 (e.g., belonging to memory cells coupledto the same wordline) are electrically insulated from each other whilethe second terminal 294 of the capacitors 290 are electrically connectedto each other through a (shared) capacitor plate or plate line at thetop of the capacitors 290 (e.g., located in the via portion of the metal7 interconnect layer). There may be separate capacitor plates forseparate arrays of capacitors 290 (e.g., one for each wordline). Thecapacitor plates may be coupled to a common voltage line (for example,in the interconnect portion of the metal 7 layer) to supply a commonvoltage to all the second terminals 294 through the capacitor plate.

The source contact of the TFT 100 is continuous and is used as thebitline 270 of the memory cell 200. The heights of the source and draincontacts can be optimized to reduce bitline capacitance (e.g., betweenthe source and drain contacts) for better sensing margins. The sourcecontacts of the TFTs 100 also serve as the bitlines of an embeddedmemory array. The dimensions of the source contacts (bitlines 270) canbe customized for lower inter-metal capacitance (e.g., by using aseparate fabrication stage to form the bitlines 270 versus thefabrication stage for this metal level in areas of the integratedcircuit outside of the memory array). Each capacitor 290 connects to adrain contact (e.g., storage node 280) of the TFT 100.

FIG. 3 is a cross-sectional (X-Z) view of an example embedded memorycell 300 having a U-shaped capacitor 390 with a recessed thin-channelTFT (such as the recessed thin-channel TFT 100 of FIG. 1), according toan embodiment of the present disclosure. Here, the embedded memory cell300 has a similar structure to that of the embedded memory cell 200 inFIG. 2, but the capacitor 390 has a U-shaped structure, with first andsecond terminals 392 and 394, and a U-shaped dielectric 396. The U-shapecan take advantage of the thicker metal interconnection layers to etch arelatively deep trench to boost capacitive surface area and capacitancewithout increasing planar area. Some of the components are the same orsimilar between the embodiments of FIGS. 2-3, and are numbered the same.For ease of discussion, their descriptions may not be repeated. Further,the materials for similarly numbered or named structures can besubstantially the same between the two embodiments.

In an array of such embedded memory cells 300, storage nodes 380 (draincontacts) of the TFTs 100 in the memory cells 300 are separated betweencells 300. Each storage node 380 is connected to a U-shaped capacitor390, such as a metal-insulator-metal (MIM) capacitor above. For example,the storage node may be one or more structures electrically connectingthe drain electrode 160 to the first terminal 392 through one or moreBEOL layers, such as the metal 5 interconnect and metal 6 via portionsof the backend processing. The capacitor 390 may be fabricated in theinterconnect portion of the metal 6 layer and the via portion of themetal 7 layer.

The capacitor 390 may be fabricated by etching (for example, byphotolithography) deep, narrow trenches in the upper portion of themetal 6 layer and the via portion of the metal 7 layer, and lining thetrenches with a thin conductor (such as first terminal 392), a thininsulator (such as dielectric 396), and another thin conductor (such assecond terminal 394), the thin insulator insulating one thin conductorfrom the other thin conductor. The capacitor 390 is fabricated in aseparate process from the rest of the metal 6 layer and metal 7 layerfabrication (to account for its large height and different electrodematerial from the rest of the metal 6 layer and metal 7 layer). Thiscreates a relatively large capacitance in the capacitor 390 by having arelatively large surface area for the terminals (e.g., first and secondterminals 392 and 394) separated by a relatively small amount ofinsulation (e.g., dielectric 396).

In further detail, in one or more embodiments of the present disclosure,the capacitor 390 is formed by etching a trench in the metal 6 layer(e.g., interconnect portion) and metal 7 layer (e.g., via portion), andsuccessively filling the trench with the three layers by, for example,atomic level deposition (ALD). For instance, the first terminal 392 canbe filled to a thickness of 20-40 nm using a conductive material (e.g.,metal, conductive metal nitride or carbide, or the like), followed by athin dielectric 396 (to increase capacitance, for example, 20-40 nm),followed by a second terminal 394 again, using metal (such as 20-40 nmthick), which can be coupled to the top electrode of every othercapacitor 390 (e.g., in an array of eDRAM memory cells). The capacitor390 can be at least 300 nm in some embodiments (e.g., for metal 5 layerson the order of 140 nm), to provide sufficient capacitance.

For example, in one embodiment, the first terminal 392 is tantalum (Ta).In another embodiment, the first terminal 392 is titanium nitride (TiN).In some embodiments, the first terminal 392 is titanium aluminum nitride(e.g., TiAlN, where the molar amount of titanium is at least that ofaluminum). In another embodiment, the first terminal 392 is tantalumaluminum carbide (TaAlC). In another embodiment, the first terminal 392is tantalum nitride (TaN). For example, in one embodiment, the secondterminal 394 is TiN. For example, in one embodiment, the dielectric 396is SiO₂. In some embodiments, such as to reduce tunneling (e.g., whenthe dielectric 396 is very thin), the dielectric 396 is a high-κdielectric material such as zirconium dioxide (ZrO₂) or aluminum oxide(Al₂O₃).

Each first terminal 392 of the capacitor 390 connects to a correspondingstorage node 380. The first terminals 392 of the capacitors 390 areelectrically insulated from each other while the second terminals 394 ofthe capacitors 390 are electrically connected to each other through a(shared) capacitor plate at the top of the capacitors 390, e.g., locatedin the via portion of the metal 7 layer. There may be separate capacitorplates for separate arrays of capacitors 390 (such as a separatecapacitor plate for each group of capacitors 390 whose correspondingthin-channel TFTs 100 are coupled to the same wordline). The capacitorplate may be coupled to a common voltage line (for example in theinterconnect portion of the metal 7 layer) to supply a common voltage toall of the second terminals 394 through the capacitor plate.

FIG. 4 is a cross-sectional (Y-Z) view of an example recessedthin-channel TFT-based embedded memory 400, according to an embodimentof the present disclosure. FIG. 4 illustrates the Y and Z dimensions(width and height, respectively), the X dimension (length) extendinginto and out of the Y-Z plane. The embedded memory 400 includes an FEOL410 that includes most of the various logic layers, circuits, anddevices to drive and control the integrated circuit (e.g., chip) beingfabricated with the embedded memory 400. As illustrated in FIG. 4, theembedded memory 400 also includes a BEOL 420 including, in this case,seven metal interconnection layers (namely, metal 1 layer 425, metal 2layer 430, metal 3 layer 435, metal 4 layer 440, metal 5 layer 445,metal 6 layer 450, and metal 7 layer 465, including metal 7 via portion455 and metal 7 interconnect portion 460) to interconnect the variousinputs and outputs of the FEOL 410.

Generally speaking, and specifically illustrated for the metal 7 layer465, each of the metal 1 layer 425 through the metal 7 layer 465includes a via portion and an interconnect portion located above the viaportion, the interconnect portion being for transferring signals alongmetal lines extending in the X or Y directions, the via portion beingfor transferring signals through metal vias extending in the Z direction(such as to the next lower metal layer underneath). Accordingly, viasconnect metal structures (e.g., metal lines or vias) from one metallayer to metal structures of the next lower metal layer. Further, eachof the metal 1 layer 425 through the metal 7 layer 465 includes apattern of conductive metal, such as copper (Cu) or aluminum (Al),formed in a dielectric medium or interlayer dielectric (ILD), such as byphotolithography.

In addition, the embedded memory 400 is further divided into a memoryarray 490 (e.g., an eDRAM memory array) built in the metal 4 layer 440through the metal 7 layer 465 and including the backend TFTs (such asrecessed thin-channel TFTs in the metal 5 layer 445) and capacitors 470(in the metal 6 layer 450 and metal 7 layer via portion 455) as well asthe wordlines (e.g., row selectors, in the metal 4 layer 440) and thebitlines (e.g., column selectors, in the metal 5 layer 445) making upthe eDRAM memory cells, and a frontend circuit including a memoryperipheral circuit 480 built in the FEOL and metal 1 layer 425 throughmetal 3 layer 435 to control (e.g., access, store, refresh) the memoryarray 490. The backend TFTs are electrically connected to the frontendcircuit.

Compared to other techniques that locate such a memory control circuitin the same layers as the memory array but in a different macro (or X-Y)area of the integrated circuit than the memory array (such as at aperiphery of the memory array), the embedded memory 400 locates thememory peripheral circuit 480 below the memory array 490 (e.g., in thesame X-Y area). This saves valuable X-Y area in the finished integratedcircuit. In further detail, the embedded memory 400 embeds thelow-leakage selector TFTs (e.g., backend TFTs including recessedthin-channel TFTs) in the metal 5 layer 445 (such as the via portion ofthe metal 5 layer 445). For example, the metal 4 layer 440 can containthe wordlines extending in the X direction to select a row of memorycells (bits) while the metal 5 layer 445 can contain the bitlinesextending in the Y direction to sense each of the memory cells (bits) inthe selected row (and to write memory data to any of the memory cells inthe selected row). The backend thin-channel TFTs can be fabricated inthe metal 5 layer 445, above the wordlines (that serve as or connect tothe gate electrodes or contacts) and below the bitlines (that serve asthe source electrodes or contacts). For example, the recessedthin-channel backend TFT can have the transistor gate below thethin-film layer (that can be formed at the bottom of the metal 5 layer445, such as in the via portion) and source and drain contacts above thethin-film layer.

In further detail, in some embodiments, the metal gate of the TFT ineach memory cell can be connected to a continuous metal 4 line below,such as a copper (Cu)-based metal line, which provides much lowerresistance compared to gate lines formed in the lower (e.g., FEOL)portions of the integrated circuit. The continuous metal 4 line is usedas the wordline of the memory array, and is covered by diffusionbarriers or diffusion barrier layers including dielectric layers, suchas silicon nitride (e.g., Si₃N₄), silicon carbide (e.g., SiC), or thelike, with vias filled with metal-diffusion barrier films like tantalumnitride (TaN), tantalum (Ta), titanium zirconium nitride (e.g.,Ti_(x)Zr_(1-X)N, such as X=0.53), titanium nitride (e.g., TiN), titaniumtungsten (TiW), or the like. A metal gate layer covers the diffusionbarrier film-filled vias, which electrically connect the copper (Cu)wordline to the metal gates of the selector TFTs, the diffusion barrierfilm preventing or helping to prevent the diffusion or migration ofcopper (Cu) from the wordline to the rest of the selector TFTs. Themetal 5 layer 445 can include an active thin-film layer (e.g., indiumgallium zinc oxide, or IGZO) and then source and drain contacts abovethe thin-film layer. The space between the source and drain contactsdetermines the gate length of the selector transistor. Athree-dimensional capacitor 470 is embedded in the metal 6 layer 450 andvia portion 455 of the metal 7 layer 465 (below the metal 7 interconnectportion 460).

FIG. 5 is an example gate length-subthreshold swing (SS) curve 510 andcomparison curve 500 for driving a recessed thin-channel TFT, accordingto an embodiment of the present disclosure. The curve 510 isrepresentative of an embodiment of the present disclosure, the TFThaving a recessed thin-channel region as described above (such as a TFTwhose channel height is half that of the source and drain heights in theactive layer, e.g., 20 nm when the source and drain region height is 40nm). The curve 500 is for a similar configuration, only no recession ofthe channel region is present (e.g., the channel region is the sameheight as the source and drain regions in the semiconductor activelayer). The x-axis of FIG. 5 tracks the gate length L_(g) of the TFT(increasing to the right, with 0 gate length being at the intersectionwith the y-axis), while the y-axis tracks the subthreshold swing (SS).SS is the ratio of the gate voltage V_(gs) to the base 10 logarithm ofthe corresponding drain-to-source current I_(DS) corresponding to thegate voltage V_(gs). Here, the gate voltage V_(gs) is held constant at agate-on voltage to keep the transistor turned on (e.g., at or nearmaximum current), while the drain-to-source current I_(DS) varies withthe gate length L_(g). The resulting SS is illustrated in the y-axis ofFIG. 5, decreasing from top to bottom, with the theoretical minimum SS(for the technology) being at the intersection of the x-axis).

As can be seen in FIG. 5, TFT performance degrades with shorter gatelength L_(g) (e.g., due to short-channel effects), but improves with therecessed channel. Put another way, a recessed channel can improveperformance of TFTs, such as by increasing the electric field of thechannel and overcoming a portion of the short-channel effects. Thisimprovement can increase with larger recession of the channel (e.g.,thinner channels), such as thin-channels whose height is less than half(e.g., one third or one quarter, such as 15 nm or 10 nm for 40 nm thicksource and drain regions) the height of the source and drain regions ofthe semiconductor (active) layer. However, this improvement onlycontinues for so long. For example, at some point, the thinner channelscan lead to device failure (e.g., over-etching the channel region duringthe recession) or decreased performance (e.g., due to factors such asincreased capacitance effects on the channel, decreased mobility of thecharge carriers, and increased resistance from the decrease incross-sectional area, to name a few).

FIGS. 6A-6G are cross-sectional (X-Z) views illustrating an examplemethod of fabricating a recessed thin-channel TFT, according to anembodiment of the present disclosure. The thin-channel TFT can be abackend TFT, such as formed as part of a BEOL process. In FIG. 6A, agate electrode 120 is formed on an interlayer dielectric (ILD) 110. Thegate 120 can include multiple components or layers, such as a wordline,a diffusion barrier layer, a metal gate, and the like. The ILD 110 caninclude etch stop or other insulating material, such as planarizingmaterial for electrically isolating structures between or within one ormore metal interconnect layers in the BEOL process. In FIG. 6A, a gatedielectric 130 is formed on the gate 120. The gate dielectric 130 can bethin, such as 4 nm, but in some embodiments may be between 3 nm and 7nm, and in some other embodiments may be between 2 nm and 10 nm. Thegate dielectric 130 may include a high-κ material such as hafniumdioxide (HfO₂). In FIG. 6C, a semiconductor layer 610 is formed on thegate dielectric 130. For example, the semiconductor layer 610 can be 40nm. In some embodiments, the semiconductor layer 610 is between 30 and60 nm. In some other embodiments, the semiconductor layer 610 is between20 nm and 80 nm. Example semiconductor layer 610 materials includeindium gallium zinc oxide (IGZO), indium zinc oxide (IZO), amorphoussilicon (a-Si), low temperature polycrystalline silicon (LTPS), andamorphous germanium (a-Ge).

In FIG. 6D, the semiconductor layer 610 is doped. More specifically, endportions of the semiconductor layer 610 are doped to form a doped layer630 including doped source and drain regions 142 and 144 while leavingundoped region 620. The doping may be sufficient to make source anddrain regions 142 and 144 conductive. In FIG. 6E, source and drainelectrodes 150 and 160 are formed over the source and drain regions 142and 144, respectively. The source and drain electrodes 150 and 160 maybe metal, such as copper interconnect, formed by a damascene processusing chemical mechanical planarization (CMP).

In FIG. 6F, the source and drain electrodes 150 and 160 are used as partof a self-aligned process to recess or thin (e.g., through etching) theundoped region 620 to form the recessed channel region 146 and completethe active layer 140. For example, half or more of the semiconductormaterial in the undoped region 620 can be removed, leaving a channelregion 146 whose height (thickness) is half or less than that of thesource and drain regions 142 and 144. In some embodiments, the removalexposes the source and drain regions 142 and 144 over the channel region146. In some embodiments, the channel region 146 is thinned down to 10nm in thickness. In other embodiments, the channel region 146 is thinnedto somewhere between 7 nm and 15 nm. In still other embodiments, thechannel region 146 is thinned to between 5 nm and 20 nm. In FIG. 6G, acapping layer (passivation layer) 170 including an insulator material isformed over the channel region 146.

The capping layer 170 can extend beyond the height of the source anddrain regions 142 and 144, partway up the source and drain electrodes150 and 160, to protect (seal) the channel region 146 and to physicallyconnect and electrically separate the source and drain regions 142 and144 as well as the source and drain electrodes 150 and 160. In someembodiments, the capping layer 170 can include one or more of aluminumoxide, silicon nitride, titanium dioxide, hafnium dioxide, siliconoxynitride, and aluminum nitride.

FIG. 7 is a schematic plan (X-Y) view of an example recessedthin-channel TFT-based embedded memory configuration, according to anembodiment of the present disclosure. The memory array configuration ofFIG. 7 includes memory cells 710 at crossing regions of wordlines 720and bitlines 730 (e.g., each memory cell 710 being driven by a uniquepair of wordline 720 and bitline 730), each memory cell 710 including arecessed thin-channel TFT 740 and a capacitor 750. Each wordline 720 isselected by a corresponding wordline driver 760, while the correspondingbitlines 730 are used to sense the state of the capacitor 750 (e.g.,logical 1 or 0) of each of the corresponding bits of the selectedwordline 720. In some embodiments, a reference column of memory cellsprovides a corresponding reference signal (e.g., halfway between a logiclow value and a logic high value) over a reference bitline 770concurrently with the sensing of the desired bit on the bitline 730.These two values are compared, by a sense amplifier 780, whichdetermines whether the desired bit is a logic high value (e.g., 1) or alogic low value (e.g., 0).

The memory cells 710 are embedded in BEOL layers (such as the highermetal interconnect layers of the BEOL) while the peripheral circuitsresponsible for memory operation, including the read sense amplifiers780 (and other bitline driver circuits) and wordline driver circuits760, are placed below the memory array (e.g., in the FEOL and lowermetal interconnect layers of the BEOL) to reduce area of the embeddedmemory.

FIG. 8A is a plan (Y-X) view of an example layout of an embedded memorywithout overlap of the memory array 490 and memory peripheral circuit(illustrated as wordline drivers 760 and column circuits 810). FIGS.8B-8C are plan (Y-X) views of an example layout or floorplan of arecessed thin-channel TFT-based embedded memory with overlap of thememory array 490 and memory peripheral circuits 760 and 810, accordingto an embodiment of the present disclosure.

The column circuits 810 (or bitline drivers) include devices such asread (bitline) sense amplifiers 780 and precharging circuits. FIG. 8Ashows the circuits spread out (e.g., occupying FEOL macro area or CMOSlogic transistor area) and without overlap. By contrast, FIG. 8B showsthe memory array 490 occupying the higher metal interconnection layersof the BEOL 420 (as illustrated in FIGS. 1-4 and 6A-7) and FIG. 8C showsthe memory peripheral circuits 760 and 810 occupying the FEOL 410 andlower metal interconnection layers of the BEOL 420 underneath the memoryarray 490 (as illustrated in FIG. 4). Since more than 35% of theembedded memory macro area can be consumed by the peripheral (memorycontrol) circuits, substantial savings of X-Y macro area can be saved byfabricating the memory arrays above the memory peripheral circuits, asin one or more embodiments of the present disclosure. Put another way,according to some embodiments of the present disclosure, an embeddedmemory is provided with memory cells only using space in the upper metallayers (e.g., metal 4 layer and above), the peripheral circuits beingmoved below the memory cells (e.g., in metal 3 layer and below,including the FEOL) and substantially reduce the memory area.

FIG. 9 illustrates an example method 900 of fabricating a recessedthin-channel TFT-based memory array (e.g., a DRAM array, such as may bepart of an eDRAM), according to an embodiment of the present disclosure.This and other methods disclosed herein may be carried out usingintegrated circuit fabrication techniques such as photolithography aswould be apparent in light of the present disclosure. The correspondingmemory cell and embedded memory including the memory cells may be partof other (logic) devices on the same substrate, such as applicationspecific integrated circuits (ASICs), microprocessors, centralprocessing units, processing cores, and the like. Unless otherwisedescribed herein, verbs such as “coupled” or “couple” refer to anelectrical coupling (such as capable of transmitting an electricalsignal), either directly or indirectly (such as through one or moreconductive layers in between).

Referring to FIG. 9 (with specific example references to the structuresof FIGS. 1-4 and 6-8) method 900 includes forming 910 a plurality ofwordlines (such as wordlines 720) extending in a first direction (suchas an X-direction), forming a plurality of bitlines (such as bitlines270 and 730) extending in a second direction (such as a Y-direction)crossing the first direction, and forming a plurality of memory cells(such as memory cells 200, 300, and 710) at crossing regions of thewordlines and the bitlines. For each memory cell, method 900 furtherincludes forming 920 a recessed thin-channel TFT (such as thin-channelTFTs 100 and 740) and a capacitor (such as capacitors 290, 470, and750).

For each thin-channel TFT, method 900 includes forming 930 a gateelectrode (such as gate 120), electrically connecting the gate electrodeto a corresponding one of the wordlines, and forming a gate dielectric(such as gate dielectric 130) on the gate electrode. For eachthin-channel TFT, method 900 further includes forming 940 asemiconductor layer (such as active layer 140) including a source region(such as source region 142) at one end and electrically connected to acorresponding one of the bitlines, and a drain region, (such as drainregion 144) at another end.

For each thin-channel TFT, method 900 further includes removing 950 aportion of the semiconductor layer between the source and drain regionsto form a semiconductor region (such as channel region 146) above and indirect contact with the gate dielectric and having less verticalthickness than the source and drain regions. See, for example, themethod of FIGS. 6A-6G for an example technique of performing such achannel recession. The semiconductor region physically connects thesource and drain regions. For each thin-channel TFT, method 900 furtherincludes forming 960 a capping layer (such as capping layer 170)including an insulator material on the recessed semiconductor region.For example, the capping layer can physically connect and electricallyseparate the source and drain regions. For each capacitor, method 900includes forming 970 a first terminal (such as first terminals 292 and392) electrically connected to the drain region of the correspondingthin-channel TFT, and forming a second terminal (such as secondterminals 294 and 394) with a dielectric medium (such as dielectricmedia 296 and 396) electrically separating the first and secondterminals.

While the above example methods appear as a series of operations orstages, it is to be understood that there is no required order to theoperations or stages unless specifically indicated. For example, invarious embodiments of method 900, for each memory cell, theelectrically connecting 940 of the source region to a corresponding oneof the bitlines can take place before, during, or after the recessing950 of the semiconductor region and the forming 960 of the second layeron the recessed semiconductor region.

Example System

FIG. 10 illustrates a computing system 1000 implemented with theintegrated circuit structures or techniques disclosed herein, accordingto an embodiment of the present disclosure. As can be seen, thecomputing system 1000 houses a motherboard 1002. The motherboard 1002may include a number of components, including, but not limited to, aprocessor 1004 (including embedded memory, such as an eDRAMincorporating recessed thin-channel TFTs as described herein) and atleast one communication chip 1006, each of which can be physically andelectrically coupled to the motherboard 1002, or otherwise integratedtherein. As will be appreciated, the motherboard 1002 may be, forexample, any printed circuit board, whether a main board, adaughterboard mounted on a main board, or the only board of system 1000,to name a few examples.

Depending on its applications, computing system 1000 may include one ormore other components that may or may not be physically and electricallycoupled to the motherboard 1002. These other components may include, butare not limited to, volatile memory (e.g., DRAM), nonvolatile memory(e.g., read-only memory (ROM), resistive random-access memory (RRAM),and the like), a graphics processor, a digital signal processor, acrypto (or cryptographic) processor, a chipset, an antenna, a display, atouchscreen display, a touchscreen controller, a battery, an audiocodec, a video codec, a power amplifier, a global positioning system(GPS) device, a compass, an accelerometer, a gyroscope, a speaker, acamera, and a mass storage device (such as hard disk drive, compact disk(CD), digital versatile disk (DVD), and so forth). Any of the componentsincluded in computing system 1000 may include one or more integratedcircuit structures or devices (e.g., one or more memory cells) formedusing the disclosed techniques in accordance with an example embodiment.In some embodiments, multiple functions can be integrated into one ormore chips (e.g., for instance, note that the communication chip 1006can be part of or otherwise integrated into the processor 1004).

The communication chip 1006 enables wireless communications for thetransfer of data to and from the computing system 1000. The term“wireless” and its derivatives may be used to describe circuits,devices, systems, methods, techniques, communications channels, and thelike, that may communicate data through the use of modulatedelectromagnetic radiation through a non-solid medium. The term does notimply that the associated devices do not contain any wires, although insome embodiments they might not. The communication chip 1006 mayimplement any of a number of wireless standards or protocols, including,but not limited to, Wi-Fi (IEEE 802.11 family), WiMAX (IEEE 802.16family), IEEE 802.20, long term evolution (LTE), Ev-DO, HSPA+, HSDPA+,HSUPA+, EDGE, GSM, GPRS, CDMA, TDMA, DECT, Bluetooth, derivativesthereof, as well as any other wireless protocols that are designated as3G, 4G, 5G, and beyond. The computing system 1000 may include aplurality of communication chips 1006. For instance, a firstcommunication chip 1006 may be dedicated to shorter range wirelesscommunications such as Wi-Fi and Bluetooth and a second communicationchip 1006 may be dedicated to longer range wireless communications suchas GPS, EDGE, GPRS, CDMA, WiMAX, LTE, Ev-DO, and others.

The processor 1004 of the computing system 1000 includes an integratedcircuit die packaged within the processor 1004. In some embodiments, theintegrated circuit die of the processor includes onboard circuitry thatis implemented with one or more integrated circuit structures or devices(e.g., one or more memory cells) formed using the disclosed techniques,as variously described herein. The term “processor” may refer to anydevice or portion of a device that processes, for instance, electronicdata from registers and/or memory to transform that electronic data intoother electronic data that may be stored in registers and/or memory.

The communication chip 1006 also may include an integrated circuit diepackaged within the communication chip 1006. In accordance with somesuch example embodiments, the integrated circuit die of thecommunication chip includes one or more integrated circuit structures ordevices (e.g., one or more memory cells) formed using the disclosedtechniques as variously described herein. As will be appreciated inlight of this disclosure, note that multi-standard wireless capabilitymay be integrated directly into the processor 1004 (e.g., wherefunctionality of any chips 1006 is integrated into processor 1004,rather than having separate communication chips). Further note thatprocessor 1004 may be a chip set having such wireless capability. Inshort, any number of processor 1004 and/or communication chips 1006 canbe used. Likewise, any one chip or chip set can have multiple functionsintegrated therein.

In various implementations, the computing device 1000 may be a laptop, anetbook, a notebook, a smartphone, a tablet, a personal digitalassistant (PDA), an ultra-mobile PC, a mobile phone, a desktop computer,a server, a printer, a scanner, a monitor, a set-top box, anentertainment control unit, a digital camera, a portable music player, adigital video recorder, or any other electronic device that processesdata or employs one or more integrated circuit structures or devices(e.g., one or more memory cells) formed using the disclosed techniques,as variously described herein.

Further Example Embodiments

The following examples pertain to further embodiments, from whichnumerous permutations and configurations will be apparent.

Example 1 is a thin-film transistor (TFT) including: a gate electrode; agate dielectric on the gate electrode; a first layer including a sourceregion, a drain region, and a semiconductor region above and in directcontact with the gate dielectric and physically connecting the sourceand drain regions, the semiconductor region having less verticalthickness than the source and drain regions; and a second layerincluding an insulator material on the semiconductor region.

Example 2 includes the TFT of Example 1, where the semiconductor regionincludes one or more of indium gallium zinc oxide (IGZO), indium zincoxide (IZO), indium tin oxide (ITO), amorphous silicon (a-Si), zincoxide, polysilicon, poly germanium, low-temperature polycrystallinesilicon (LTPS), amorphous germanium (a-Ge), indium arsenide, copperoxide, and tin oxide.

Example 3 includes the TFT of Example 2, where the semiconductor regionincludes one or more of IGZO, IZO, a-Si, LTPS, and a-Ge.

Example 4 includes the TFT of any of Examples 1-3, where the insulatormaterial includes one or more of aluminum oxide, gallium oxide, siliconnitride, silicon dioxide, titanium dioxide, hafnium dioxide, siliconoxynitride, aluminum silicate, tantalum oxide, hafnium tantalum oxide,aluminum nitride, aluminum silicon nitride, sialon, zirconium dioxide,hafnium zirconium oxide, tantalum silicate, and hafnium silicate.

Example 5 includes the TFT of Example 4, where the insulator materialincludes one or more of aluminum oxide, silicon nitride, titaniumdioxide, hafnium dioxide, silicon oxynitride, and aluminum nitride.

Example 6 includes the TFT of any of Examples 1-5, where the thicknessof the semiconductor region is no more than half that of the source anddrain regions.

Example 7 includes the TFT of any of Examples 1-6, where the thicknessof the semiconductor region is between 5 and 20 nanometers (nm).

Example 8 includes the TFT of any of Examples 1-7, where the secondlayer physically connects and electrically separates the source anddrain regions.

Example 9 includes the TFT of Example 8, further including source anddrain electrodes electrically connected to the source and drain regions,respectively, where the second layer physically connects andelectrically separates the source and drain electrodes.

Example 10 includes the TFT of any of Examples 1-9, where the gatedielectric includes a high-κ dielectric.

Example 11 includes the TFT of Example 10, where the high-κ dielectricincludes hafnium dioxide.

Example 12 includes the TFT of Example 11, where the gate dielectric hasa thickness between 2 and 10 nanometers (nm).

Example 13 is a memory cell including: the TFT of any of Examples 1-12,the gate electrode being electrically connected to a wordline and thesource region being electrically connected to a bitline; and a capacitorincluding a first terminal electrically connected to the drain region, asecond terminal, and a dielectric medium electrically separating thefirst and second terminals.

Example 14 is a memory array including a plurality of wordlinesextending in a first direction, a plurality of bitlines extending in asecond direction crossing the first direction, and a plurality of memorycells at crossing regions of the wordlines and the bitlines, the memorycells including a first memory cell and a second memory cell, each ofthe first and second memory cells having a structure of the memory cellof Example 13, with the wordline being a corresponding one of thewordlines and the bitline being a corresponding one of the bitlines.

Example 15 is a backend TFT including the TFT of any of Examples 1-14,the backend TFT being electrically connected to a frontend circuit.

Example 16 is an embedded memory cell including: the backend TFT ofExample 15, the gate electrode being electrically connected to awordline and the source region being electrically connected to abitline; and a capacitor including a first terminal electricallyconnected to the drain region, a second terminal, and a dielectricmedium electrically separating the first and second terminals.

Example 17 includes the embedded memory cell of Example 16, where thefrontend circuit includes a wordline driver electrically connected tothe wordline and a sense amplifier electrically connected to thebitline.

Example 18 is an embedded memory including a plurality of wordlinesextending in a first direction, a plurality of bitlines extending in asecond direction crossing the first direction, and a plurality ofembedded memory cells at crossing regions of the wordlines and thebitlines, the embedded memory cells including a first embedded memorycell and a second embedded memory cell, each of the first and secondembedded memory cells having a structure of the embedded memory cell ofany of Examples 16-17, with the wordline being a corresponding one ofthe wordlines and the bitline being a corresponding one of the bitlines.

Example 19 includes the embedded memory of Example 18, where thefrontend circuit includes a plurality of wordline drivers electricallyconnected to the wordlines and a plurality of sense amplifierselectrically connected to the bitlines.

Example 20 is a memory cell including: a thin-film transistor (TFT)including a gate electrode electrically connected to a wordline, a gatedielectric on the gate electrode, an active layer on the gate dielectricand having a source region, a drain region electrically connected to abitline, and a semiconductor region physically connecting the source anddrain regions, the semiconductor region having less vertical thicknessthan the source and drain regions, and a capping layer on thesemiconductor region and physically connecting the source and drainregions; and a capacitor including a first terminal electricallyconnected to the drain region, a second terminal, and a dielectricmedium electrically separating the first and second terminals.

Example 21 includes the memory cell of Example 20, where thesemiconductor region includes one or more of indium gallium zinc oxide(IGZO), indium zinc oxide (IZO), indium tin oxide (ITO), amorphoussilicon (a-Si), zinc oxide, polysilicon, poly germanium, low-temperaturepolycrystalline silicon (LTPS), amorphous germanium (a-Ge), indiumarsenide, copper oxide, and tin oxide.

Example 22 includes the memory cell of Example 21, where thesemiconductor region includes one or more of IGZO, IZO, a-Si, LTPS, anda-Ge.

Example 23 includes the memory cell of any of Examples 20-22, where thecapping layer includes one or more of aluminum oxide, gallium oxide,silicon nitride, silicon dioxide, titanium dioxide, hafnium dioxide,silicon oxynitride, aluminum silicate, tantalum oxide, hafnium tantalumoxide, aluminum nitride, aluminum silicon nitride, sialon, zirconiumdioxide, hafnium zirconium oxide, tantalum silicate, and hafniumsilicate.

Example 24 includes the memory cell of Example 23, where the cappinglayer includes one or more of aluminum oxide, silicon nitride, titaniumdioxide, hafnium dioxide, silicon oxynitride, and aluminum nitride.

Example 25 includes the memory cell of any of Examples 20-24, where thethickness of the semiconductor region is no more than half that of thesource and drain regions.

Example 26 includes the memory cell of any of Examples 20-25, where thethickness of the semiconductor region is between 5 and 20 nanometers(nm).

Example 27 includes the memory cell of any of Examples 20-26, where thecapping layer electrically separates the source and drain regions.

Example 28 includes the memory cell of Example 27, further includingsource and drain electrodes electrically connected to the source anddrain regions, respectively, where the capping layer physically connectsand electrically separates the source and drain electrodes.

Example 29 includes the memory cell of any of Examples 20-28, where thegate dielectric includes a high-κ dielectric.

Example 30 includes the memory cell of Example 29, where the high-κdielectric includes hafnium dioxide.

Example 31 includes the memory cell of Example 30, where the gatedielectric has a thickness between 2 and 10 nanometers (nm).

Example 32 is a memory array including a plurality of wordlinesextending in a first direction, a plurality of bitlines extending in asecond direction crossing the first direction, and a plurality of memorycells at crossing regions of the wordlines and the bitlines, the memorycells including a first memory cell and a second memory cell, each ofthe first and second memory cells having a structure of the memory cellof any of Examples 20-31, with the wordline being a corresponding one ofthe wordlines and the bitline being a corresponding one of the bitlines.

Example 33 is an embedded memory cell including the memory cell of anyof Examples 20-31, the TFT being a backend TFT electrically connected toa frontend circuit, the frontend circuit including a wordline driverelectrically connected to the wordline and a sense amplifierelectrically connected to the bitline.

Example 34 is an embedded memory including a plurality of wordlinesextending in a first direction, a plurality of bitlines extending in asecond direction crossing the first direction, and a plurality ofembedded memory cells at crossing regions of the wordlines and thebitlines, the embedded memory cells including a first embedded memorycell and a second embedded memory cell, each of the first and secondembedded memory cells having a structure of the embedded memory cell ofExample 33, with the wordline being a corresponding one of the wordlinesand the bitline being a corresponding one of the bitlines.

Example 35 includes the embedded memory of Example 34, where thefrontend circuit further includes a plurality of wordline driverselectrically connected to the wordlines, and a plurality of senseamplifiers electrically connected to the bitlines.

Example 36 is a method of fabricating a thin-film transistor (TFT), themethod including: forming a gate electrode; forming a gate dielectric onthe gate electrode; forming a first layer including a source region, adrain region, and a semiconductor region above and in direct contactwith the gate dielectric and physically connecting the source and drainregions, the semiconductor region having less vertical thickness thanthe source and drain regions; and forming a second layer including aninsulator material on the semiconductor region.

Example 37 includes the method of Example 36, where the forming of thefirst layer includes: forming a semiconductor layer on the gatedielectric; and removing a portion of the semiconductor layer betweenthe source and drain regions to form the semiconductor region.

Example 38 includes the method of Example 37, where the removing of theportion of the semiconductor layer includes removing at least half ofthe semiconductor layer between the source and drain regions.

Example 39 includes the method of any of Examples 37-38, where theremoving of the portion of the semiconductor layer includes recessingthe semiconductor layer so that the thickness of the semiconductorregion is between 5 and 20 nanometers (nm).

Example 40 includes the method of any of Examples 37-39, where theforming of the first layer further includes forming source and drainelectrodes on and electrically connected to the source and drainregions, respectively, and the removing of the portion of thesemiconductor layer includes recessing an exposed portion of thesemiconductor layer between the formed source and drain electrodes.

Example 41 includes the method of Example 40, where the forming of thesecond layer includes forming the insulator material on thesemiconductor region to physically connect and electrically separate thesource and drain electrodes.

Example 42 includes the method of any of Examples 36-41, where thesemiconductor region includes one or more of indium gallium zinc oxide(IGZO), indium zinc oxide (IZO), indium tin oxide (ITO), amorphoussilicon (a-Si), zinc oxide, polysilicon, poly germanium, low-temperaturepolycrystalline silicon (LTPS), amorphous germanium (a-Ge), indiumarsenide, copper oxide, and tin oxide.

Example 43 includes the method of Example 42, where the semiconductorregion includes one or more of IGZO, IZO, a-Si, LTPS, and a-Ge.

Example 44 includes the method of any of Examples 36-43, where theinsulator material includes one or more of aluminum oxide, galliumoxide, silicon nitride, silicon dioxide, titanium dioxide, hafniumdioxide, silicon oxynitride, aluminum silicate, tantalum oxide, hafniumtantalum oxide, aluminum nitride, aluminum silicon nitride, sialon,zirconium dioxide, hafnium zirconium oxide, tantalum silicate, andhafnium silicate.

Example 45 includes the method of Example 44, where the insulatormaterial includes one or more of aluminum oxide, silicon nitride,titanium dioxide, hafnium dioxide, silicon oxynitride, and aluminumnitride.

Example 46 includes the method of any of Examples 36-45, where thesecond layer physically connects and electrically separates the sourceand drain regions.

Example 47 includes the method of any of Examples 36-46, where the gatedielectric includes a high-κ dielectric.

Example 48 includes the method of Example 47, where the high-κdielectric includes hafnium dioxide.

Example 49 includes the method of Example 48, where the gate dielectrichas a thickness between 2 and 10 nanometers (nm).

Example 50 is a method of fabricating a memory cell, the methodincluding: fabricating the TFT by the method of any of Examples 36-49;electrically connecting the gate electrode to a wordline; electricallyconnecting the source region being to a bitline; forming a capacitorincluding first and second terminals, and a dielectric mediumelectrically separating the first and second terminals; and electricallyconnecting the first terminal to the drain region.

Example 51 is a method of fabricating a memory array, the methodincluding: forming a plurality of wordlines extending in a firstdirection; forming a plurality of bitlines extending in a seconddirection crossing the first direction; and forming a plurality ofmemory cells at crossing regions of the wordlines and the bitlines, thememory cells including a first memory cell and a second memory cell,each of the first and second memory cells being fabricated by the methodof Example 50, with the wordline being a corresponding one of thewordlines and the bitline being a corresponding one of the bitlines.

Example 52 is a method of fabricating a backend TFT, the methodincluding: fabricating the TFT by the method of any of Examples 36-49;and electrically connecting the TFT to a frontend circuit.

Example 53 is a method of fabricating an embedded memory cell, themethod including: fabricating the backend TFT by the method of Example52; electrically connecting the gate electrode to a wordline;electrically connecting the source region to a bitline; forming acapacitor including first and second terminals, a second terminal, and adielectric medium electrically separating the first and secondterminals; and electrically connecting the first terminal to the drainregion.

Example 54 includes the method of Example 53, where the frontend circuitincludes a wordline driver and a sense amplifier, and the method furtherincludes electrically connecting the wordline to the wordline driver andthe bitline to the sense amplifier.

Example 55 is a method of fabricating an embedded memory, the methodincluding: forming a plurality of wordlines extending in a firstdirection; forming a plurality of bitlines extending in a seconddirection crossing the first direction; and forming a plurality ofembedded memory cells at crossing regions of the wordlines and thebitlines, the embedded memory cells including a first embedded memorycell and a second embedded memory cell, each of the first and secondembedded memory cells being fabricated by the method of any of Examples53-54, with the wordline being a corresponding one of the wordlines andthe bitline being a corresponding one of the bitlines.

Example 56 includes the method of Example 55, where the frontend circuitincludes a plurality of wordline drivers and a plurality of senseamplifiers, and the method further includes electrically connecting thewordlines to the wordline drivers and the bitlines to the senseamplifiers.

Example 57 is an integrated circuit (IC) structure including: a gateelectrode; a gate dielectric on the gate electrode; a semiconductorregion above and in direct contact with the gate dielectric; a cappingstructure on the semiconductor region; and a source region and a drainregion each adjacent to a different portion of and having a greatervertical thickness than the semi conductor region.

Example 58 includes the IC structure of Example 57, where thesemiconductor region includes one or more of indium gallium zinc oxide(IGZO), indium zinc oxide (IZO), indium tin oxide (ITO), amorphoussilicon (a-Si), zinc oxide, polysilicon, poly germanium, low-temperaturepolycrystalline silicon (LTPS), amorphous germanium (a-Ge), indiumarsenide, copper oxide, and tin oxide.

Example 59 includes the IC structure of Example 58, where thesemiconductor region includes one or more of IGZO, IZO, a-Si, LTPS, anda-Ge.

Example 60 includes the IC structure of any of Examples 57-59, where thecapping structure includes one or more of aluminum oxide, gallium oxide,silicon nitride, silicon dioxide, titanium dioxide, hafnium dioxide,silicon oxynitride, aluminum silicate, tantalum oxide, hafnium tantalumoxide, aluminum nitride, aluminum silicon nitride, sialon, zirconiumdioxide, hafnium zirconium oxide, tantalum silicate, and hafniumsilicate.

Example 61 includes the IC structure of Example 60, where the cappingstructure includes one or more of aluminum oxide, silicon nitride,titanium dioxide, hafnium dioxide, silicon oxynitride, and aluminumnitride.

Example 62 includes the IC structure of any of Examples 57-61, where thethickness of the semiconductor region is no more than half that of thesource region or the drain region.

Example 63 includes the IC structure of any of Examples 57-62, where thethickness of the semiconductor region is between 5 and 20 nanometers(nm).

Example 64 includes the IC structure of any of Examples 57-63, where thegate dielectric includes a high-κ dielectric.

Example 65 includes the IC structure of Example 64, where the high-κdielectric includes hafnium dioxide.

Example 66 includes the IC structure of Example 65, where the gatedielectric has a thickness between 2 and 10 nanometers (nm).

Example 67 includes the IC structure of any of Examples 57-66, where thecapping structure physically connects and electrically separates thesource and drain regions.

Example 68 includes the IC structure of Example 67, further includingsource and drain electrodes electrically connected to the source anddrain regions, respectively, where the capping structure physicallyconnects and electrically separates the source and drain electrodes.

The foregoing description of example embodiments has been presented forthe purposes of illustration and description. It is not intended to beexhaustive or to limit the present disclosure to the precise formsdisclosed. Many modifications and variations are possible in light ofthis disclosure. It is intended that the scope of the present disclosurebe limited not by this detailed description, but rather by the claimsappended hereto. Future filed applications claiming priority to thisapplication may claim the disclosed subject matter in a differentmanner, and may generally include any set of one or more limitations asvariously disclosed or otherwise demonstrated herein.

What is claimed is:
 1. An integrated circuit (IC) structure comprising:a gate electrode; a gate dielectric on the gate electrode; a regioncomprising semiconductor material above and in direct contact with thegate dielectric; a structure on the region comprising semiconductormaterial, the structure comprising insulator material; and a sourceregion and a drain region each comprising semiconductor material andadjacent to a different portion of the region comprising semiconductormaterial, the source and drain regions each having a greater verticalthickness than the region, such that at least a portion of the structureis laterally between respective portions of the source and drainregions, wherein the gate electrode extends vertically beneath thesource region and the drain region.
 2. The IC structure of claim 1,wherein the semiconductor region comprises one or more of indium,gallium, zinc, tin, oxygen, amorphous silicon (a-Si), polysilicon, polygermanium, low-temperature polycrystalline silicon (LTPS), amorphousgermanium (a-Ge), arsenic, and copper.
 3. The IC structure of claim 1,wherein the semiconductor region comprises one or more of indium galliumzinc oxide (IGZO), indium zinc oxide (IZO), amorphous silicon (a-Si),low-temperature polycrystalline silicon (LTPS), and amorphous germanium(a-Ge).
 4. The IC structure of claim 1, wherein the structure comprisesone or more of aluminum, gallium, silicon, titanium, hafnium, tantalum,sialon, zirconium, oxygen, and nitrogen.
 5. The IC structure of claim 1,wherein the structure comprises one or more of aluminum oxide, siliconnitride, titanium dioxide, hafnium dioxide, silicon oxynitride, andaluminum nitride.
 6. The IC structure of claim 1, wherein the thicknessof the region comprising semiconductor material is no more than halfthat of the source region or the drain region.
 7. The IC structure ofclaim 1, wherein the thickness of the region comprising semiconductormaterial is between 5 and 20 nanometers (nm).
 8. The IC structure ofclaim 1, wherein the gate dielectric comprises a high-K dielectric. 9.The IC structure of claim 8, wherein the high-.kappa. dielectriccomprises hafnium and oxygen.
 10. The IC structure of claim 9, whereinthe gate dielectric has a thickness between 2 and 10 nanometers (nm).11. The IC structure of claim 1, further comprising source and drainelectrodes electrically connected to the source and drain regions,respectively, wherein the structure physically connects and electricallyseparates the source and drain electrodes.
 12. A thin-film transistor(TFT) comprising: a gate electrode; a gate dielectric on the gateelectrode; a first layer comprising semiconductor material and includinga source region, a drain region, and a region between the source anddrain regions, the first layer above and in direct contact with the gatedielectric, the region having less vertical thickness than the sourceand drain regions, wherein the gate electrode extends vertically beneaththe source region and the drain region; and a second layer including aninsulator material on the region, the second layer being at leastpartially between the source and drain regions and completely above theregion between the source and drain regions.
 13. A memory cellcomprising: the TFT of claim 12, the gate electrode being electricallyconnected to a wordline and the source region being electricallyconnected to a bitline; and a capacitor including a first terminalelectrically connected to the drain region, a second terminal, and adielectric medium electrically separating the first and secondterminals.
 14. A memory array comprising a plurality of wordlinesextending in a first direction, a plurality of bitlines extending in asecond direction orthogonal to the first direction, and a plurality ofmemory cells each between crossing regions of corresponding wordlinesand the bitlines, the memory cells including a first memory cell and asecond memory cell, each of the first and second memory cells having astructure of the memory cell of claim 13, with the wordline being acorresponding one of the wordlines and the bitline being a correspondingone of the bitlines.
 15. An embedded memory cell comprising: a backendTFT of claim 12, the backend TFT being electrically connected to afrontend circuit, the gate electrode being electrically connected to awordline and the source region being electrically connected to abitline; and a capacitor including a first terminal electricallyconnected to the drain region, a second terminal, and a dielectricmedium electrically separating the first and second terminals.
 16. Theembedded memory cell of claim 15, wherein the frontend circuit comprisesa wordline driver electrically connected to the wordline and a senseamplifier electrically connected to the bitline.
 17. An embedded memorycomprising a plurality of wordlines extending in a first direction, aplurality of bitlines extending in a second direction crossing the firstdirection, and a plurality of embedded memory cells at crossing regionsof the wordlines and the bitlines, the embedded memory cells including afirst embedded memory cell and a second embedded memory cell, each ofthe first and second embedded memory cells having a structure of theembedded memory cell of claim 15, with the wordline being acorresponding one of the wordlines and the bitline being a correspondingone of the bitlines.
 18. The embedded memory of claim 17, wherein thefrontend circuit comprises a plurality of wordline drivers electricallyconnected to the wordlines and a plurality of sense amplifierselectrically connected to the bitlines.
 19. An integrated circuit (IC)structure comprising: a gate electrode; a gate dielectric on the gateelectrode; a first region, a second region, and a third region, eachcomprising semiconductor material and being above and in direct contactwith the gate dielectric, wherein the second region is directly betweenthe first and third regions, and the first and third regions each have agreater vertical thickness than the second region, wherein the gateelectrode extends vertically beneath the first region and the thirdregion; a structure on the second region and comprising insulatormaterial, such that at least a portion of the structure is betweenrespective sidewalls of the first and third regions; and a sourceelectrode above and on the first region, and a drain electrode above andon the third region.
 20. The IC structure of claim 19, wherein thefirst, second, and third regions are part of an active layer of a thinfilm transistor.